MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors) are used as switching devices in electronic circuits such as inverter circuits and converter circuits. MOSFETs include a parasitic PN junction diode (body diode) as a bipolar device. In an electronic circuit in which a MOSFET is used, when a current flows through a parasitic PN junction diode (body diode) of the MOSFET, the properties of the device may deteriorate. Specifically, when a current flows through the PN junction diode, an electron-hole recombination may occur at a crystal fault, if it exists in the MOSFET, to result in an expansion of the crystal fault.
In particular, in an SiC-MOSFET prepared with semiconductor materials mainly including SiC, when a current flows through a PN junction diode, a forward deterioration occurs. More specifically, it is known that a crystal fault called Basal Plane Dislocation (BPD) exists in an SiC semiconductor crystal. The crystal structure at the BPD is different from those in other portions, that is, the band gap of the crystal is smaller than the inherent band gap of the SiC semiconductor. The BPD is therefore likely to be an electron-hole recombination center. Accordingly, when a forward current flows through the PN joint portion, the BPD expands to be a planar fault (stacking fault). This leads to an increase in the on-resistance of the SiC-MOSFET.
In order to prevent a current from flowing through a PN junction diode, a circuit configuration has hence been proposed in which a Schottky barrier diode having an operating voltage lower than that of the PN junction diode is connected in parallel to the PN junction diode.